/Engine/Plugins/Runtime/XRBase/Source/XRBase/Public/HeadMountedDisplayFunctionLibrary.h
Grabs the current orientation and position for the HMD. If positional tracking is not available, DevicePosition will be a zero vector
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintPure, Category="Input|HeadMountedDisplay") static void GetOrientationAndPosition ( FRotator & DeviceRotation, FVector & DevicePosition )